Stripped thread where bottom bolt of serp belt tensioner goes. Please Advise

Hi Guys, any advice would be great. This is for a 95 M3.

So I was torquing down the bottom bolt of the hydraulic tensioner (the one for the serpentine belt) and to my knowledge, per my Bentley Manual the bolt is an M8.8 and thus 18 ft/lbs of torque would be ok... I barely got a few turns in (nowhere near enough to be 18 ft/lbs) and it spun...? I took out the bolt and saw that I stripped maybe 2-3 threads.

So the bolt was flush even when spinning, which means it couldnt grab any more thread right? in other words, its too short? but then again BMW made it that way for a reason...? Im thinking go to the dealer and get a few bolts that are the same diameter maybe just a little bit longer to just secure it in place. What do you guys think?

Also, is the thread I stripped in the base plate? or on the engine block? :/

Thanks in advance!

I attached a few pictures for reference.